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1 | /*! |
2 | @file | |
3 | Defines `boost::hana::intersperse`. | |
4 | ||
f51cf556 | 5 | Copyright Louis Dionne 2013-2022 |
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6 | Distributed under the Boost Software License, Version 1.0. |
7 | (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt) | |
8 | */ | |
9 | ||
10 | #ifndef BOOST_HANA_INTERSPERSE_HPP | |
11 | #define BOOST_HANA_INTERSPERSE_HPP | |
12 | ||
13 | #include <boost/hana/fwd/intersperse.hpp> | |
14 | ||
15 | #include <boost/hana/at.hpp> | |
16 | #include <boost/hana/bool.hpp> | |
17 | #include <boost/hana/concept/sequence.hpp> | |
18 | #include <boost/hana/config.hpp> | |
19 | #include <boost/hana/core/dispatch.hpp> | |
20 | #include <boost/hana/core/make.hpp> | |
21 | #include <boost/hana/length.hpp> | |
22 | ||
23 | #include <cstddef> | |
24 | #include <utility> | |
25 | ||
26 | ||
1e59de90 | 27 | namespace boost { namespace hana { |
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28 | //! @cond |
29 | template <typename Xs, typename Z> | |
30 | constexpr auto intersperse_t::operator()(Xs&& xs, Z&& z) const { | |
31 | using S = typename hana::tag_of<Xs>::type; | |
32 | using Intersperse = BOOST_HANA_DISPATCH_IF(intersperse_impl<S>, | |
33 | hana::Sequence<S>::value | |
34 | ); | |
35 | ||
36 | #ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS | |
37 | static_assert(hana::Sequence<S>::value, | |
38 | "hana::intersperse(xs, z) requires 'xs' to be a Sequence"); | |
39 | #endif | |
40 | ||
41 | return Intersperse::apply(static_cast<Xs&&>(xs), static_cast<Z&&>(z)); | |
42 | } | |
43 | //! @endcond | |
44 | ||
45 | template <typename S, bool condition> | |
46 | struct intersperse_impl<S, when<condition>> : default_ { | |
47 | template <std::size_t i, typename Xs, typename Z> | |
48 | static constexpr decltype(auto) | |
49 | pick(Xs&&, Z&& z, hana::false_ /* odd index */) | |
50 | { return static_cast<Z&&>(z); } | |
51 | ||
52 | template <std::size_t i, typename Xs, typename Z> | |
53 | static constexpr decltype(auto) | |
54 | pick(Xs&& xs, Z&&, hana::true_ /* even index */) | |
55 | { return hana::at_c<(i + 1) / 2>(static_cast<Xs&&>(xs)); } | |
56 | ||
57 | template <typename Xs, typename Z, std::size_t ...i> | |
58 | static constexpr auto | |
59 | intersperse_helper(Xs&& xs, Z&& z, std::index_sequence<i...>) { | |
60 | return hana::make<S>( | |
61 | pick<i>(static_cast<Xs&&>(xs), static_cast<Z&&>(z), | |
62 | hana::bool_c<(i % 2 == 0)>)... | |
63 | ); | |
64 | } | |
65 | ||
66 | template <typename Xs, typename Z> | |
67 | static constexpr auto apply(Xs&& xs, Z&& z) { | |
68 | constexpr std::size_t size = decltype(hana::length(xs))::value; | |
69 | constexpr std::size_t new_size = size == 0 ? 0 : (size * 2) - 1; | |
70 | return intersperse_helper(static_cast<Xs&&>(xs), static_cast<Z&&>(z), | |
71 | std::make_index_sequence<new_size>{}); | |
72 | } | |
73 | }; | |
1e59de90 | 74 | }} // end namespace boost::hana |
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75 | |
76 | #endif // !BOOST_HANA_INTERSPERSE_HPP |